"Bacteria is added to the urine which breaks it down into the ammonium nitrate that plants need to grow."

Why that extra processing step? Soil bacteria do the urea→ammonia step just fine. Not to mention that urea is a very safe & stable compound.

Another issue is the possibility of spreading pathogens. A gardener can deal with this by just letting the urine sit for a # of months. But perhaps that's not a good approach for an industrial process?

Btw. "pee" in the url - nice touch. :)